The proposed study seeks to explain longitudianl variation in natality in the United States since World War II. The theoretical basis of the research draws on previous work that has isolated those aspects of social and economic structure most relevant to natality(the study excludes social psychological variables). These major sets of independent variables are: 1) Current economic conditions of young adults relative to expectations, 2) Sex roles and associated phenomena, 3) Urbanization, education and other chanracteristics that could be regarded as aspectsof economic development and 4) The practical availability of contraception and abortion. These four sets of variables originate from different theoretical perspectives and could be regarded as competing explanations. This research begins with the assumption that they are likely to be important to an explanation of important changes in antality and moves in the direction of the construction and testing of a causal model of the major relationships linking this cluster of social, economic and demographic variables. It is suggected that only in this way can one learnwhich relationships are most important and which, if any, are neglible or incorrectly hypothesized. The methodology of path analysis will be utilized in the proposed research. It is necessary, however, to adapt the normal procedures somewhat in order to analyze changes over time.